1. Field of the Invention
The present invention relates to a technique for detecting a rotational misalignment between respective substrates of a bonded substrate in which a plurality of disk-like substrates such as semiconductor wafers each having a notch formed in an outer edge portion thereof is stacked on top of each other and bonded together.
2. Description of the Related Art
With the increases in speed and capacity of semiconductor chips, recently, a technique is known for bonding together a plurality of semiconductor wafers and providing wiring between top and bottom wafers with a through silicon via (TSV). Bonding semiconductor wafers together in this manner requires a technique for accurately bonding the semiconductor wafers to each other in a bonding process. In other words, the semiconductor wafers must be accurately positioned. In order to do so, diameters and center positions of the semiconductor wafers must be accurately measured and positioning of the semiconductor wafers must be performed using the measurements.
Japanese Patent Application Laid-open No. H07-218228 describes a method of measuring a diameter of a single semiconductor wafer and Japanese Patent Application Laid-open No. H01-098908 describes a method of detecting a rotational misalignment of a single semiconductor wafer. Japanese Patent Application Laid-open No. 2009-032802 describes a method of measuring a rotation angle of each of a plurality of semiconductor wafers that has been bonded together by observing a contour of each semiconductor wafer and calculating a notch direction.
However, since the method described in Japanese Patent Application Laid-open No. H07-218228 is a method of obtaining a diameter using a measured distance value from a center of a semiconductor wafer to an orientation flat, a measurement with high accuracy cannot be expected. The method described in Japanese Patent Application Laid-open No. H01-098908 requires that a grating-like pattern be created in advance on a semiconductor wafer. In addition, the method described in Japanese Patent Application Laid-open No. 2009-032802 is used for measurement after a bonded wafer has been thinned and cannot be used for measurement at the time of bonding.
Furthermore, when a notch indicating a crystal orientation is formed on an outer edge portion of a semiconductor wafer, bonding is performed by conforming notch positions to each other. However, when a minute positional misalignment occurs during a bonding process, there were no conventional means to detect such a positional misalignment at a micron level.